Bottas and Zhou both endured a disappointing qualifying session on Saturday in Montreal.
Bottas qualified 17th after narrowly missing the cut to Q2, while his Chinese team-mate was further behind in 20th following a lack of running in FP1 and contact with the wall in FP3, which put him on the back foot for qualifying.
Because both cars are already far behind on the grid for what is expected to be a race in mixed weather conditions, Sauber has taken the opportunity to make car changes in parc ferme.
Both Bottas and Zhou have reverted to an older specification of rear wing, which under parc ferme rules means they are forced to start from the pitlane.
Sauber had brought a new rear wing this weekend with a reduced flap and redesigned main plane for the low-drag requirements of the Circuit Gilles Villeneuve, which also came with a different beam wing, but the Swiss team has now gone back to an older design.
Bottas' car has also been fitted with a third energy store and a third set of control electronics, breaching the maximum allocation of two components allowed for the season.
That would have netted the Finn a grid penalty, but that has now been absorbed by the pitlane start.
"Qualifying confirms that we are lacking performance in the single lap," Sauber team representative Alessandro Alunni Bravi stated.
"We have already seen in the last races that our main competitors took a step forward, pushing us to the bottom of the midfield in terms of qualifying pace.
"The race will be once again difficult for us, and we must maximise every opportunity that may arise.
"We have previously shown that we can deliver a better race pace, but we can’t hide the fact that it’s another difficult weekend for us. Still, we’ll do our best to improve our position.”
Sauber, which in a transitional phase before morphing into the Audi factory team in 2026, is currently the only team without points on the board in 2024, languishing in 10th and last place of the constructors' table.
